Given the huge increase in the availability of copyrighted digital products in recent years, much importance has been placed on developing technology that adequately protects the right of the copyright holder to fully control the recording of duplicates of the digital product (hereafter, simply “product”). Particular interest has been focused on improving methods of embedding as a watermark on both the product and duplicates of the product, information that protects the copyright.
A watermark is information that has been multiplexed onto selected areas of main product data, or “content,” of the product (note: data headers, control information, etc, do not qualify as content). The multiplexing process involves an ID code being assigned to the content. Take, for example, an ID code of “10010110 . . . ” and content being image data. In this case, the value of each pixel of image data is matched with a corresponding bit of the ID code in order from the top left corner. If the value of the pixel and the bit of ID code are matched then the value of the pixel is used unaltered, and if not matched then the pixel is assigned a new value being the same as the bit of ID code.
Image data having information multiplexed as a watermark is generated by repeating this process for all the bits of the ID code. Given the difficulty in identifying the actual areas in the content that have been multiplexed, it is common to refer to the multiplexed information as having been “embedded” on the product.
In the above example, the value of each pixel of image data is matched with a corresponding bit of the ID code in order from the top left corner. The ID code can, however, be broken up and arranged randomly, making it even more difficult to locate where in the content the information has been embedded. Copyright protection information embedded as a watermark on the product in this manner is thus well concealed, and the possibility of the embedded information being tampered with or altered is extremely remote.
Further information relating to watermark technology including the advantages and various embedding methods is available from the following references:                MATSUI Kineo, The Basics of Watermarks, Morikita Pub, 1998.        INOUE Akira, Watermarks—Encryption Systems for the Multimedia Age, Maruyama Gakugei Pub, 1997.        “Watermarks Protecting the Multimedia Age,” in Nikkei Electronics, 24 Feb. 1997.        
Currently, the most common type of information embedded as a watermark is a copy attribute, otherwise referred to as “copy generation information.” There are four basic levels of copy attribute: “copy free” permitting unlimited recording of duplicates, “one generation copy” limiting the recording of duplicates to one generation, “no more copy” prohibiting a further recording of duplicates, and “never copy” prohibiting all recording of duplicates. A typical operation of a recording control employing a copy attribute will now be described with reference to FIG. 1.
In FIG. 1 the recording apparatus is a personal computer 81 that records a product downloaded from a public network 82. The product has a copy attribute embedded as a watermark thereon and the personal computer 81 records a duplicate of the product onto a recording medium in accordance with the embedded copy attribute. The recording medium in FIG. 1 is a recordable optical disc, being a DVD-RAM, DVD-R, or DVD-RW, etc.
If the embedded copy attribute shows “no more copy” (arrow y1) or “never copy” (arrow y2) then the recording of the duplicate onto the disc is cancelled, and if “copy free” (arrow y3) is shown then duplicates of the product are freely recorded.
A duplicate can also be recorded onto the disc if the embedded copy attribute shows “one generation copy” (arrow y4), but not before the copy attribute has been changed into a copy attribute showing “no more copy” and the new copy attribute has been embedded as a watermark on the duplicate. Thus the recording of duplicates can be limited to personal-use duplicates, and the spirit of Article 30 of the Japanese Copyright Act, which allows a limited number of duplicates to be recorded without the specific permission of the copyright holder, is not violated. A typical operation of a reproduction control employing a copy attribute will now be described with reference to FIG. 2.
In FIG. 2 the reproduction apparatus is a DVD player 83 and the image recorded on the disc is reproduced on a display 84. If the recording medium is a read-only disc, being a CD-ROM, DVD-RAM, etc, having a product recorded thereon, then the DVD-player 83 conducts the reproduction unconditionally. However, if the recording medium is a recordable disc having a duplicate of a product recorded thereon, then the DVD-player 83 refers to the copy attribute embedded as a watermark on the duplicate in order to judge whether the duplicate should be reproduced.
If the copy attribute embedded on the duplicate shows “never copy” (arrow y5) then reproduction of the duplicate is canceled since it is reasonable to assume that the duplicate has been improperly recorded. A legitimate recording apparatus would not have recorded a duplicate of a product embedded with a copy attribute showing “never copy.”
A copyright infringement is also assumed if the embedded copy attribute shows “one generation copy” (arrow y6) since this copy attribute should have been changed to a copy attribute showing “no more copy” and the new copy attribute should then have been embedded as a watermark on the duplicate.
On the other hand, the reproduction apparatus permits the reproduction of the duplicate when the embedded copy attribute shows either “copy free” (arrow y7) or “no more copy” (arrow y8).
In practice, however, the use of existing copyright protection technology to embed a copy attribute showing “one generation copy” as a watermark on the product has proved inadequate in preventing copyright infringements since illegitimate copy machines can be used to record improper duplicates. When a duplicate is recorded onto a disc by a legitimate recording apparatus it is normal for the duplicate to occupy multiple sectors of the disc. However, when improper duplicates are recorded using an illegitimate copy machine, data is read in sectors from each of the occupied sectors of a disc designated as the source disc and then the read data is written, again in sectors, onto a target disc, this procedure being repeated for all of the sectors of the source disc. Duplicates recorded in this manner are known as “dead copies.”
FIG. 3 shows a process by which dead copies are recorded using an illegitimate copy machine. In FIG. 3 the personal computer 81 stores a product downloaded from the public network 82. If the copy attribute embedded on the product shows “one generation copy,” a duplicate of the product is generated, the copy attribute is changed into a copy attribute showing “no more copy,” and the new copy attribute is embedded as a watermark on the generated duplicate. The duplicate is then recorded onto a recordable disc 86 (arrow y4).
A copyright infringement occurs when the disc 86, having recorded thereon the duplicate embedded with the copy attribute showing “no more copy,” is designated as the source disc (arrow y9) and a duplicate of the duplicate, referred to as a second-generation duplicate, is recorded in sector units onto a target disc (arrow y10) by an illegitimate copy machine. This improper recording process results in a disc 87 having the second-generation duplicate recorded thereon. Discs 88 (arrow y11) and 89 (arrow y12) are generated through a repetition of this process.
The reproduction apparatus will reproduce the improperly recorded discs 87, 88 and 89 normally when instructed to do so, since they all are embedded with the copy attribute showing “no more copy.” Thus unlimited second-generation duplicates can be recorded of the product embedded with a copy attribute showing “one generation copy,” and the copyright of the product is effectively rendered worthless.
The recording of dead copies does not even require a specialized copy machine since an ordinary personal computer can be equipped to carry out the improper recording process simply by installing an exclusive copy seal. When dead copies are recorded using a personal computer, data is firstly read from each of the occupied sectors on the source disc and then stored on the internal memory or the hard disk of the computer. The stored data is then written onto corresponding sectors of the target disc, this procedure being repeated for all sectors of the source disc. Improved methods of embedding copyright protection information are thus needed in order to prevent copyright infringements resulting from the simple generation of dead copies.